1. Field of the Invention
The present invention relates to an insulated gate bipolar transistor and method for manufacturing the same, especially to a high-performance insulated gate bipolar transistor and method for manufacturing the same.
2. Description of Prior Art
Insulated gate bipolar transistor (IGBT) is a semiconductor device combining the features of metal-oxide-semiconductor field effect transistor (MOSFET) and bipolar junction transistor (BJT). IGBT has the advantages of gate-controlling ability of MOSFET and low turn-on voltage of BJT and is thus extensively used in high voltage and high power applications.
A conventional IGBT, such as a punch through (PT) IGBT, mainly comprises a P+ type semiconductor substrate and N-type buffer layer arranged thereon. An N type epitaxial layer is formed on the N-type buffer layer and functions as drain of parasitic MOSFET in the IGBT. Moreover, a gate and an emitter are formed in the N type epitaxial layer, and a collector is formed on bottom face of the P+ type substrate. The breakdown voltage of the PT IGBT is determined by the P+ type substrate and N-type buffer layer because a maximum electric field is generated therebetween.
Another conventional IGBT, such as a non-punch through (NPT) IGBT, does not use N-type buffer layer. The breakdown voltage of the NPT IGBT is determined by the avalanche mechanism of the N type epitaxial (N drift) layer. To increase the breakdown voltage, field stop (FS) IGBT was developed, where the N-type buffer layer in PT IGBT is replaced by a field stop ion implantation layer. Therefore, the abrupt junction in the PT IGBT is also replaced by a graded (such as a linearly graded) N type profile. The value of the maximum electric field can be advantageously reduced to enhance breakdown voltage.
However, in above-mentioned three types of IGBTs, a fast return epitaxial diode (FRED) is needed to parallel connect with the IGBT to release turn-off current. Therefore, a reverse-conducted diode is built-in above mentioned IGBTs for soft switching. This kind of IGBT is referred to as reverse conduction field stop (RCFS) IGBT. The conventional RCFS IGBT is first formed with N+ type doped layer on backside of substrate by using metal mask, then formed with P+ type doped layer functioning as collector, and finally formed with N+ type doped layer and P type doped layer by rapid thermal annealing. Nevertheless, lateral Zener diode tends to form in the RCFS because the N+ doped layer and the P type doped layer are on the same horizontal plane of the backside of the substrate.